Quemoy and Matsu. Their possession had been contested ever since Mainland China fell to the Communists and the former government of China set up shop on Taiwan in 1949. At the time, Mainland China wasn't recognized by the the United States or the U.N. and Taiwan, or Free China as it was known, was.

So when the Mainland Chinese launched a series of bombings and a threatened invasion on the islands of Quemoy and Matsu in September of 1958, the Domino theory of Communist conquest came into full play, and The U.S. was quickly drawn into the conflict, prompting President Eisenhower to go before the American people and explain what was going on and what we were potentially about to get ourselves into.

Pres. Eisenhower: “Congress has made clear its recognition that the security of the Western Pacific is vital to the security of the United States, and that we should be firm. The Senate has ratified by overwhelming vote, security treaties with The Republic of China, covering Formosa and The Pescadores, and also the Republic of Korea. We have a mutual security treaty with the Republic of The Philippines which, situated so close as it is to Formosa, could be next in line for conquest if Formosa into hostile hands.”

The crisis eventually simmered down, with Mainland China backing away from a full-on shooting war. But it certainly didn't end the saber rattling that went on in the region.

Then again, Vietnam was on slow simmer at the time.